The invention relates to a device for the reception/transmission of electromagnetic waves.
Interactive cordless telecommunication services are developing rapidly. These services relate to telephones, faxes, television, especially digital television, the field called xe2x80x9cmultimediaxe2x80x9d and the internet array. The equipment for these major broadcasting services must be available at a reasonable cost. The same applies, in particular to the receiver/transmitter of the user who has to communicate with a server, most often via a telecommunications satellite. Generally these communications are carried out in the ultrahigh frequency range. For example the C band is used, from 3.7 GHz to 4.2 GHz (3.4 GHz to 4.2 GHz in the extended C band) for reception and from 6.4 GHz to 6.7 GHz for transmission.
In these frequency ranges, it is usually possible to use a waveguide receiver and a waveguide transmitter, the two waveguides being separate.
Implementation of this technology is expensive if a return link from the user to the base station has to be ensured for the purpose of routing information flow or user commands to the source of the service (for example, in the field of audiovisual programming or pay per view). It is therefore costly. Furthermore, its weight and size are incompatible with use by individuals.
Document U.S. Pat. No. 5,041,840 (Cipolla et al.) describes a device having two coaxial waveguides exciting a horn whose radiating aperture is coplanar with an array of radiating patches. The array has the same phase centre as the horn. Thus the transmission and reception directions of the device may be coincident.
However, the unit comprising the array and the radiating aperture takes up too large an area in the array plane. The size problem is not solved.
The invention remedies the aforementioned drawback.
To this end, the subject of the invention is an electromagnetic wave reception/transmission device, comprising a body, characterized in that it combines:
a reception circuit board incorporated in the body, comprising a first array of n radiating elements with a microstrip structure for receiving electromagnetic waves in a first frequency band,
electromagnetic wave transmission means with longitudinal radiation defining a radiation axis for the transmission of electromagnetic waves in a second frequency band, the said means comprising excitation means for exciting longitudinal radiation means,
the said transmission means being of nearly constant cross section in the body, perpendicularly intersecting the reception circuit board in a circular aperture around which the said radiating elements are symmetrically arranged,
the said reception and transmission means being laid out so that their respective phase centres lie approximately in a so-called focusing region.
Such a hybrid device (that is to say with waveguide technology and microstrip technology) is feasible at reasonable cost. Its, size and weight are reduced. Excellent isolation between the transmission and reception signals is obtained. Furthermore, use of longitudinal radiation means has the advantage of a broad frequency band for transmission. Above all it should be noted that the use of such a longitudinal radiation means of constant cross section allows the area occupied by these means in the reception circuit board plane to be limited compared with a horn, which makes reception and transmission in close frequency bands possible and which also enables radiating elements to be moved closer together, therefore reducing the number n of radiating elements. Typically the device according to the invention enables a ratio between the central frequencies of the respective transmission and reception bands of less than or equal to three to be obtained, as will be shown at the end of the present application.
According to one embodiment, the said focusing region is reduced to a point forming the phase centre of the said device.
Advantageously, the said radiation means comprise a dielectric rod with longitudinal radiation whose axis is coincident with the transmission radiation axis.
According to one embodiment, the said excitation means comprise a waveguide.
According to one embodiment, the said radiation means comprise a helical device having a series of turns.
In this case, the said excitation means can be pictured as a coaxial line.
According to one embodiment, n is equal to 4.
According to one embodiment, the said dielectric rod has the shape of a cylinder with conical ends.
According to one embodiment, the said excitation means are coupled to a microstrip transmission circuit board laid out in a straight section of the excitation means in the body for transmission of electromagnetic waves.
According to one embodiment, the device according to the invention has a pair of probes arranged on the transmission circuit board and at right angles to each other and capable of transmitting orthogonally polarized waves.
According to one embodiment, the microstrip transmission circuit board has a frequency conversion circuit.
According to one embodiment, the microstrip reception circuit board has a frequency conversion circuit.
According to one embodiment, the device, according to the invention has an intermediate circuit board having at least part of the frequency conversion circuit associated with the reception circuit board and/or the transmission circuit board.
According to one embodiment, an auxiliary circuit board is associated in a parallel manner with the reception circuit board and has a second array comprising a plurality of radiating elements opposite the respective radiating elements of the first array and of resonant frequency close to the resonant frequency of the first array so that the pair of arrays of radiating elements opposite each other is equivalent to a single array with an extended bandwidth.
According to one embodiment, the waveguide is closed by a quarter-wave (xcexGT/4) cavity of length equal to a quarter of the wavelength (xcexGT) of the guided wave transmitted.
The subject of the invention is also an electromagnetic wave reception/transmission system having a means for focusing waves, characterized in that it is fitted with a device according to the invention.
Advantageously, the said focusing means have a reflector, which is preferably parabolic, and the device is laid out in such a way that the said focusing region nearly coincides with the focus of the said reflector, the said device thus operating as the primary source of the system.
An additional advantage is that the said focusing means have an electromagnetic lens and that the said device is laid out in such a way that the said focusing region nearly coincides with the focus of the said electromagnetic lens, the said device thus operating as the primary source of the system.